Early September 1862 . . . Gen. Robert E. Lee's Army of Northern Virginia crosses the Potomac River and invades the North for the first time during the Civil War. Maj. Gen. George B. McClellan's Army of the Potomac moves northwest through Maryland in pursuit of the Confederates. Lee decides on a daring course of action. To capture the Union garrison at Harpers Ferry, the Confederate commander boldly divides his army. Meanwhile in one of the greatest intelligence coups of the war, two Federal soldiers find a copy of Lee's orders. The Confederate plan in hand, the Union commander brings the Southern army to battle along Antietam Creek. Lee's men are badly outnumbered, and their backs are to the Potomac River, but McClellan, incredibly, fritters away his advantage in a series of bloody, piecemeal attacks. Both sides suffer horrific casualties, and the Battle of Antietam ends in a gruesome stalemate. Two days later, Lee recrosses the Potomac and retreats into Virginia. Although the Battle of Antietam ended in a bloody draw, it ultimately proved to be an important Union victory. Southern hopes for aid from Britain and France waned, and soon after Lee's retreat, President Lincoln issued the Emancipation Proclamation. A momentous battle, artfully recreated by an important military historian.